[FLINK] Fix print connector: write to stdout/stderr instead of file

[ggjh-159]

fix: apache/gluten#12306
related pr: bigo-sg/velox4j#39 apache/gluten#12320

Summary

The print connector wrote rows through a dwio Writer against a file path resolved by the planner (<logdir>/taskmanager.out). Under multi-parallelism every subtask opened the same file, and the writer truncated it on open — output from N-1 subtasks was lost, and the surviving stream was interleaved without serialization.

This PR switches the sink to write to std::cout / std::cerr (TM stdout is already redirected to taskmanager.out by Flink) and removes the file plumbing:

• PrintSink no longer owns a dwio Writer. appendData() formats each row via StringFormatter into a std::stringstream and, guarded by a process-wide std::mutex, writes prefix_ + body + '\n' to the stream selected by isStdErr_.
• PrintSink::computePrefix(printIdentifier, parallelism, taskIndex) mirrors Flink's PrintSinkOutputWriter.open() prefix logic: empty when parallelism == 1, otherwise <printIdentifier>:<taskIndex+1>> (or <taskIndex+1>> when the identifier is empty, <printIdentifier>> when parallelism is 1 and the identifier is non-empty).
• PrintTableHandle drops path and gains printIdentifier / isStdErr. serialize() now emits a "name": "PrintTableHandle" discriminator so the Java side (velox4j PolymorphicDeserializer) can round-trip the handle.
• Constructor reads parallelism / task_index from ConnectorQueryCtx::sessionProperties() via a lambda IIFE in the member-init list, so the prefix is const and computed exactly once.

Test

• UTs
• End-to-end via the companion gluten-flink PR (parallelism.default = 2, nexmark q0, 10000 events): every bid row reaches <logdir>/flink-*-taskexecutor-x-*.out, no truncation, and each line carries the 1> / 2> subtask prefix.

[KevinyhZou]

LGTM